Radical-radical reactions of superoxide: a potential route to toxicity

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Direct Evidence of a Light-Dependent Sink of Superoxide within Chromophoric Dissolved Organic Matter

Superoxide (O2• -) is produced photochemically in natural waters by chromophoric dissolved organic matter (CDOM) via the reaction of molecular oxygen with photoproduced one-electron reductants (OERs) within CDOM. In the absence of other sinks (metals or organic radicals), O2• - is believed to undergo primarily dismutation to produce hydrogen peroxide (H2O2). However, past studies have implicated the presence of an additional light-dependent sink of O2• - that does not lead to H2O2 production. Here, we provide direct evidence of this sink through O2• - injection experiments. During irradiations, spikes of O2• - are consumed to a greater extent (∼85-30% loss) and are lost much faster (up to ∼0.09 s-1) than spikes introduced post-irradiation (∼50-0% loss and ∼0.03 s-1 rate constant). The magnitude of the loss during irradiation and the rate constant are wavelength-dependent. Analysis of the H2O2 concentration post-spike indicates that this light-dependent sink does not produce H2O2 at low spike concentrations. This work further demonstrates that simply assuming that the O2• - production is twice the H2O2 production is not accurate, as previously believed.

Oyster ferritin can efficiently alleviate ROS-mediated inflammation attributed to its unique micro-environment around three-fold channels

The conversion of toxic Fe²⁺ into non-toxic Fe³⁺ stored in the inner cavity of ferritin nanocage could effectively reduce the occurrence of the Fenton reaction and inhibit the formation of harmful reactive oxygen species (ROS). In this study, we reveal that oyster ferritin (GF1) can rely on its high catalytic activity (7.7 times that of rHuHF) and high binding ability of Fe²⁺ (9.1 times that of rHuHF) to reduce the precursors of Fenton reaction, thus inhibiting the occurrence of Fenton reaction and slowing down reactive oxygen species-mediated inflammation. The above significant advantage of GF1 can be attributed to the Asp at the position 120th, which could increase the negatively charged area of three-fold channels from 37.8% (rHuHF) to 67.8% and then enhance its oxidation rate and ability of GF1. The findings are of great value in advancing novel nanoparticle drug design based on crystalline structure.

Superoxide Anion Chemistry-Its Role at the Core of the Innate Immunity

Classically, superoxide anion O₂^•- and reactive oxygen species ROS play a dual role. At the physiological balance level, they are a by-product of O₂ reduction, necessary for cell signalling, and at the pathological level they are considered harmful, as they can induce disease and apoptosis, necrosis, ferroptosis, pyroptosis and autophagic cell death. This revision focuses on understanding the main characteristics of the superoxide O₂^•-, its generation pathways, the biomolecules it oxidizes and how it may contribute to their modification and toxicity. The role of superoxide dismutase, the enzyme responsible for the removal of most of the superoxide produced in living organisms, is studied. At the same time, the toxicity induced by superoxide and derived radicals is beneficial in the oxidative death of microbial pathogens, which are subsequently engulfed by specialized immune cells, such as neutrophils or macrophages, during the activation of innate immunity. Ultimately, this review describes in some depth the chemistry related to O₂^•- and how it is harnessed by the innate immune system to produce lysis of microbial agents.

Superoxide: The enigmatic chemical chameleon in neutrophil biology

The burst of superoxide produced when neutrophils phagocytose bacteria is the defining biochemical feature of these abundant immune cells. But 50 years since this discovery, the vital role superoxide plays in host defense has yet to be defined. Superoxide is neither bactericidal nor is it just a source of hydrogen peroxide. This simple free radical does, however, have remarkable chemical dexterity. Depending on its environment and reaction partners, superoxide can act as an oxidant, a reductant, a nucleophile, or an enzyme substrate. We outline the evidence that inside phagosomes where neutrophils trap, kill, and digest bacteria, superoxide will react preferentially with the enzyme myeloperoxidase, not the bacterium. By acting as a cofactor, superoxide will sustain hypochlorous acid production by myeloperoxidase. As a substrate, superoxide may give rise to other forms of reactive oxygen. We contend that these interactions hold the key to understanding the precise role superoxide plays in neutrophil biology. State-of-the-art techniques in mass spectrometry, oxidant-specific fluorescent probes, and microscopy focused on individual phagosomes are needed to identify bactericidal mechanisms driven by superoxide. This work will undoubtably lead to fascinating discoveries in host defense and give a richer understanding of superoxide's varied biology.

Decrease of glutathione peroxidase in arrhythmic cardiac pathology in young individuals and its therapeutic implications

Glutathione peroxidase (GPx), as an antioxidant enzyme, is involved in the regulation of processes that cause cellular oxidative stress, with implications in various pathologies. The aim of the present study was to evaluate GPx variations in patients with arrhythmic, non-structural cardiac disorders. The research was performed on 120 patients, with a mean age of 33 years old, divided into 3 equal groups, of which 2 groups included patients with cardiac arrhythmias, the first group, associated with dyslipidemia and the second one, without dyslipidemia, and a control group consisting of healthy individuals. The method for determining GPx was based on the GPx enzyme catalysis reaction of the reduced glutathione (GSH) oxidation reaction by cumene hydroperoxide. The results revealed that GPx variation was decreased in patients with cardiac arrhythmias, with or without dyslipidemia, up to 66 and 74% of mean control values, respectively, the differences being statistically significant, showing the existence of an oxidative stress imbalance, that may be involved in triggering arrhythmogenic electrochemical mechanisms. The GPx deficiency determined in relation to cardiac arrhythmias was in dyslipidemic and non-lipidemic patients as follows: 29-35% in sinus bradycardia, 31-35% in associated cardiac arrhythmias, 30-33% in sinus tachycardia, 27-33% in atrial fibrillation, 32-33% in atrial flutter, 27-32% in atrial extrasystolic arrhythmia, 28-30% in ventricular extrasystolic arrhythmia and 18-26% in paroxysmal supraventricular tachycardia. Collectively, the results revealed that GPx, an antioxidant enzyme, is a specific biomarker, whose decrease indicated the existence of oxidative stress in young individuals with cardiac arrhythmias and its involvement in arrhythmogenic electrochemical processes. In addition, GPx deficiencies were between 18-35% in all types of cardiac arrhythmias, the highest being recorded in sinus bradycardia and the lowest in paroxysmal supraventircular tachycardia. Furthermore, the oxidative stress favored by the decrease of GPx induced lipid oxidation, regardless of the presence or absence of dyslipidemia, which triggered the formation of anti-lipid antibodies and a subclinical endothelial aggression, with early atherosclerotic potential. GPx evaluation may argue for the existence of oxidative stress in non-structural cardiac arrhythmias, and by its proper correction (antioxidants), prophylaxis of atherogenic dysfunction.

Prediction of reaction mechanism for OH radical-mediated phenol oxidation using quantum chemical calculation

Understanding the reaction mechanism of OH•-mediated oxidation of organic micropollutants (OMPs) contributes to the assessment and development of advanced oxidation processes (AOPs) for removal of OMPs in water environment. In this study, a theoretical approach using quantum chemical calculation (QCC) was employed to investigate the prediction accuracy of the reaction mechanism (i.e., reaction site and rate) for OH•-mediated oxidation of phenol, where the hydroquinone and catechol are generated as transformation products (TPs) via radical and electrophilic reactions. We compared three different levels of theory (Hartree-Fock, B3LYP, and M06-2X) with 6-311 + G (2d,2p)/SMD, and the reaction site and rate constants were predicted by the Fukui function and transition state theory, respectively. Overall, the prediction accuracy of the TPs formation mechanism was the highest in the calculations using M06-2X. For example, the initial OH• addition to phenol was predicted to occur with a probability of 77% for the ortho position and 23% for the para position, which was consistent with the experimental observation. By applying the transition state theory, the rate constants toward TPs formation pathway can be reasonably reproduced, suggesting that M06-2X has an effective function for polycyclic reactions. However, the observed discrepancies in rate constants are inferred from dispersion effects and the multi-reference property in the computational system or derived from mismatch of target reactions between theoretical calculations and experiments. Overall, this study provides an insight into QCC application for investigating the formation mechanism of TPs in AOPs for removal of OMPs in water environment.

Photoproduction Rates of One-Electron Reductants by Chromophoric Dissolved Organic Matter via Fluorescence Spectroscopy: Comparison with Superoxide and Hydrogen Peroxide Rates

One-electron reductants (OER) photoproduced by chromophoric dissolved organic matter (CDOM) have been shown to be likely precursors for the formation of superoxide and subsequently hydrogen peroxide. An improved method that employs a nitroxide radical probe (3AP) has been developed and utilized to determine the photoproduction rates of OER from a diverse set of CDOM samples. 3AP reacts with OER to produce the hydroxylamine, which is then derivatized with fluorescamine and quantified spectrofluorometrically. Although less sensitive than traditional methods for measuring R_O2•-, measuring R_H provides a simpler and faster method of estimating R_O2•- and is amenable to continuous measurement via flow injection analysis. Production rates of OER (R_H), superoxide (R_O2•-), and hydrogen peroxide (R_H2O2) have a similar wavelength dependence, indicating a common origin. If all the OER react with molecular oxygen to produce superoxide, then the simplest mechanism predicts that R_H/R_H2O2 and R_O2•-/R_H2O2 should be equal to 2. However, our measurements reveal R_H/R_H2O2 values as high as 16 (5.7-16), consistent with prior results, and R_O2•-/R_H2O2 values as high as 8 (5.4-8.2). These results indicate that a substantial fraction of superoxide (65-88%) is not undergoing dismutation. A reasonable oxidative sink for superoxide is reaction with photoproduced phenoxy radicals within CDOM.

Regulation of the epigenetic landscape by immune cell oxidants

Excessive production of microbicidal oxidants by neutrophils can damage host tissue. The short-term response of cells to oxidative stress is well understood, but the mechanisms behind long-term consequences require further clarification. Epigenetic pathways mediate cellular adaptation, and are therefore a potential target of oxidative stress. Indeed, there is evidence that many proteins and metabolites involved in epigenetic pathways are redox sensitive. In this review we provide an overview of the epigenetic landscape and discuss the potential for redox regulation. Using this information, we highlight specific examples where neutrophil oxidants react with epigenetic pathway components. We also use published data from redox proteomics to map out known intersections between oxidative stress and epigenetics that may signpost helpful directions for future investigation. Finally, we discuss the role neutrophils play in adaptive pathologies with a focus on tumour initiation and progression. We hope this information will stimulate further discourse on the emerging field of redox epigenomics.

Chemical repair mechanisms of damaged tyrosyl and tryptophanyl residues in proteins by the superoxide radical anion

Even though reaction of the superoxide anion radical/hydroperoxide radical could lead to oxidation of biomolecules, it can repair oxidized tyrosyl and tryptophanyl residues in proteins at diffusion-controlled rates.

Catalysis of Peroxide Reduction by Fast Reacting Protein Thiols

Life on Earth evolved in the presence of hydrogen peroxide, and other peroxides also emerged before and with the rise of aerobic metabolism. They were considered only as toxic byproducts for many years. Nowadays, peroxides are also regarded as metabolic products that play essential physiological cellular roles. Organisms have developed efficient mechanisms to metabolize peroxides, mostly based on two kinds of redox chemistry, catalases/peroxidases that depend on the heme prosthetic group to afford peroxide reduction and thiol-based peroxidases that support their redox activities on specialized fast reacting cysteine/selenocysteine (Cys/Sec) residues. Among the last group, glutathione peroxidases (GPxs) and peroxiredoxins (Prxs) are the most widespread and abundant families, and they are the leitmotif of this review. After presenting the properties and roles of different peroxides in biology, we discuss the chemical mechanisms of peroxide reduction by low molecular weight thiols, Prxs, GPxs, and other thiol-based peroxidases. Special attention is paid to the catalytic properties of Prxs and also to the importance and comparative outlook of the properties of Sec and its role in GPxs. To finish, we describe and discuss the current views on the activities of thiol-based peroxidases in peroxide-mediated redox signaling processes.

Mechanism of the Formation of Electronically Excited Species by Oxidative Metabolic Processes: Role of Reactive Oxygen Species

It is well known that biological systems, such as microorganisms, plants, and animals, including human beings, form spontaneous electronically excited species through oxidative metabolic processes. Though the mechanism responsible for the formation of electronically excited species is still not clearly understood, several lines of evidence suggest that reactive oxygen species (ROS) are involved in the formation of electronically excited species. This review attempts to describe the role of ROS in the formation of electronically excited species during oxidative metabolic processes. Briefly, the oxidation of biomolecules, such as lipids, proteins, and nucleic acids by ROS initiates a cascade of reactions that leads to the formation of triplet excited carbonyls formed by the decomposition of cyclic (1,2-dioxetane) and linear (tetroxide) high-energy intermediates. When chromophores are in proximity to triplet excited carbonyls, the triplet-singlet and triplet-triplet energy transfers from triplet excited carbonyls to chromophores result in the formation of singlet and triplet excited chromophores, respectively. Alternatively, when molecular oxygen is present, the triplet-singlet energy transfer from triplet excited carbonyls to molecular oxygen initiates the formation of singlet oxygen. Understanding the mechanism of the formation of electronically excited species allows us to use electronically excited species as a marker for oxidative metabolic processes in cells.

Superoxide radicals react with peptide-derived tryptophan radicals with very high rate constants to give hydroperoxides as major products

Oxidative damage is a common process in many biological systems and proteins are major targets for damage due to their high abundance and very high rate constants for reaction with many oxidants (both radicals and two-electron species). Tryptophan (Trp) residues on peptides and proteins are a major sink for a large range of biological oxidants as these side-chains have low radical reduction potentials. The resulting Trp-derived indolyl radicals (Trp^•) have long lifetimes in some circumstances due to their delocalized structures, and undergo only slow reaction with molecular oxygen, unlike most other biological radicals. In contrast, we have shown previously that Trp^• undergo rapid dimerization. In the current study, we show that Trp^• also undergo very fast reaction with superoxide radicals, O₂^•-, with k 1-2 × 10⁹ M^-1 s^-1. These values do not alter dramatically with peptide structure, but the values of k correlate with overall peptide positive charge, consistent with positive electrostatic interactions. These reactions compete favourably with Trp^• dimerization and O₂ addition, indicating that this may be a major fate in some circumstances. The Trp^• + O₂^•- reactions occur primarily by addition, rather than electron transfer, with this resulting in high yields of Trp-derived hydroperoxides. Subsequent degradation of these species, both stimulated and native decay, gives rise to N-formylkynurenine, kynurenine, alcohols and diols. These data indicate that reaction of O₂^•- with Trp^• should be considered as a major pathway to Trp degradation on peptides and proteins subjected to oxidative damage.

Superoxide dismutase protects ribonucleotide reductase from inactivation in yeast

Ribonucleotide reductase (RNR) catalyses the rate limiting step of DNA synthesis utilising a mechanism that requires a tyrosyl radical. We have previously shown that superoxide can quench protein tyrosyl radicals in vitro, either by oxidative addition, or reduction of the radical to tyrosine. Here, we observe that Saccharomyces cerevisiae strains lacking either copper-zincSOD (SOD1) or manganese SOD (SOD2) had decreased RNR activity compared to SOD-competent yeast. When superoxide production was increased by treatment with paraquat, RNR activity was further decreased, with yeast lacking SOD1 being the most sensitive. The growth of yeast lacking SOD1 was also the most sensitive to paraquat treatment. Using expressed recombinant RNR, superoxide addition was not detectable using mass-spectrometry. This suggests that oxidative addition is not the major route of inhibition in our system, but does not rule out reduction by superoxide as a possible mechanism. Our results demonstrate that protection of RNR from inactivation by superoxide is an important function of SOD, particularly cytoplasmic SOD1.

Tetrabromobisphenol A induces cellular damages in pancreatic β-cells in vitro

Tetrabromobisphenol A (TBBPA) is a well-known organobrominated flame retardant. TBBPA has been detected in the environment. The roles played by environmental pollutants in increasing the prevalence of metabolic syndrome are attracting increasing concern. In the present work, we investigated the effects of TBBPA on rat pancreatic β-cells (the RIN-m5F cell line). RIN-m5F cells were incubated with different concentrations of TBBPA for 48 h, and cell viability and the extent of apoptosis were determined. We also measured the levels of inflammatory cytokines, reactive oxygen species (ROS), mitochondrial adenosine triphosphate (ATP), and cardiolipin, as well as the extent of cytochrome c release from mitochondria. TBBPA reduced the ATP level, induced cardiolipin peroxidation and cytochrome c release, and triggered apoptotic cell death. Moreover, TBBPA increased the levels of inflammatory cytokines (TNF-α and IL-1β), nitric oxide, intracellular ROS, and mitochondrial superoxide. Together, our results indicate that TBBPA damages pancreatic β-cells by triggering mitochondrial dysfunction and inducing apoptosis.

Estimation of Oxidative Stress Involvement by Superoxide Dismutase Variation in Cardiac Arrhythmias

Cardiac arrhythmias, commonly diagnosed in young people, involve multiple etiopathogenic factors, including oxidative stress.

PURPOSE

Evaluation of superoxide dismutase (SOD) variations as an antioxidant enzyme (with a physiological role in the dismutation of highly reactive oxygen free radicals into oxygen and water) in young patients with cardiac arrhythmias.

MATERIAL AND METHOD

The study was conducted on a group of 40 young patients with a mean age of 34 years old, of both sexes, with non-lesional cardiac dysrhythmias, compared to a control group of 40 healthy subjects, determining for both groups the SOD serum level. Diagnosis of cardiac rhythm disorder was supported by electrocardiogram, imaging and laboratory investigations.

RESULTS

SOD recorded a 61% decrease of mean values in patients compared to controls. The decreasing variation was found in all arrhythmia types, as follows: atrial fibrillation (51,54%), sinus bradycardia (54,86%), atrial flutter (55,71%), extrasystolic ventricular arrhythmia (64,20%), extrasystolic atrial arrhythmia (65,27%), combined arrhythmias (65,93%), supraventricular paroxysmal tachycardia (71,32%) and sinus tachycardia (74,24%). SOD deficiency demonstrates the involvement of oxidative stress in cardiac arrhythmic pathogenesis, excess oxygen radicals interfering with multiple mechanisms related to the onset of arrhythmogenesis. The SOD decrease was more important in females (60,57%) than in males (67,06%) and in those with nutrition poor in antioxidants.

CONCLUSIONS

SOD estimation represents a biomarker whose decrease and deficiency implies occurrence of oxidative stress and implicitly highlights its role in cardiac arrhythmic pathology in young people, with the possibility of monitoring and correction by pharmacological or non-pharmacological therapeutic means.

Free radicals and polyphenols: The redox chemistry of neurodegenerative diseases

The oxidation of bioorganic materials by air and, particularly, the oxidative stress involved in the cell loss and other pathologies associated with neurodegenerative diseases (NDs) are of enormous social and economic importance. NDs generally involve free radical reactions, beginning with the formation of an initiating radical by some redox, thermal or photochemical process, causing nucleic acid, protein and lipid oxidations and the production of harmful oxidative products. Physically, persons afflicted by NDs suffer progressive loss of memory and thinking ability, mood swings, personality changes, and loss of independence. Therefore, the development of antioxidant strategies to retard or minimize the oxidative degradation of bioorganic materials has been, and still is, of paramount importance. While we are aware of the importance of investigating the biological and medical aspects of the diseases, elucidation of the associated chemistry is crucial to understanding their progression, heading to intelligent chemical intervention to find more efficient therapies to prevent or delay the onset of the diseases. Accordingly, this review aims to provide the reader with a chemical base to understand the behavior and properties of the reactive oxygen species involved and of typical radical scavengers such as polyphenolic antioxidants. Some discussion on the structures of the various species, their formation, chemical reactivities and lifetimes is included. The ultimate goal is to understand how, when and where they form, how far they travel prior to react, which molecules are their targets, and how we can, eventually, control their activity to minimize their impact by means of chemical methods. Recent strategies explore chemical modifications of the hydrophobicity of potent, natural antioxidants to improve their efficiency by fine-tuning their concentrations at the reaction site.

Novel Biomarkers of Heart Failure

Although substantial improvements have been made in majority of cardiac disorders, heart failure (HF) remains a major health problem, with both increasing incidence and prevalence over the past decades. For that reason, the number of potential biomarkers that could contribute to diagnosis and treatment of HF patients is, almost exponentially, increasing over the recent years. The biomarkers that are, at the moment, more or less ready for use in everyday clinical practice, reflect different pathophysiological processes present in HF. In this review, seven groups of biomarkers associated to myocardial stretch (mid-regional proatrial natriuretic peptide, MR-proANP), myocyte injury (high-sensitive troponins, hs-cTn; heart-type fatty acid-binding protein, H-FABP; glutathione transferase P1, GSTP1), matrix remodeling (galectin-3; soluble isoform of suppression of tumorigenicity 2, sST2), inflammation (growth differentiation factor-15, GDF-15), renal dysfunction (neutrophil gelatinase-associated lipocalin, NGAL; kidney injury molecule-1, KIM-1), neurohumoral activation (adrenomedullin, MR-proADM; copeptin), and oxidative stress (ceruloplasmin; myeloperoxidase, MPO; 8-hydroxy-2'-deoxyguanosine, 8-OHdG; thioredoxin 1, Trx1) in HF will be overviewed. It is important to note that clinical value of individual biomarkers within the single time points in both diagnosis and outcome prediction in HF is limited. Hence, the future of biomarker application in HF lies in the multimarker panel strategy, which would include specific combination of biomarkers that reflect different pathophysiological processes underlying HF.

Dietary Probiotic Bacillus subtilis Strain fmbj Increases Antioxidant Capacity and Oxidative Stability of Chicken Breast Meat during Storage

This study was aimed to measure the dietary effects of probiotic Bacillus subtilis strain fmbj (BS fmbj) on antioxidant capacity and oxidative stability of chicken breast meat during storage. Treatment groups were fed the basal diet with BS fmbj at 0 g/kg (CON), 0.2 g/kg (BS-1), 0.3 g/kg (BS-2), or 0.4 g/kg (BS-3) doses without antibiotics. During 8 days of storage at 4°C, BS-2 group showed a significant improvement (P < 0.05) on meat quality (pH, Drip loss, Cooking loss, Shear force, color L*, a*, b*), free radical scavenging activity (DPPH, ABTS⁺, H₂O₂), tissues antioxidant enzyme capacity (SOD, CAT, GSH-Px, GSH, T-SH), mitochondria antioxidant enzyme capacity (MnSOD, GPx, GSH), mRNA expression of antioxidant genes (Nrf2, HO-1, SOD, CAT, GSH-Px) and mitochondrial function genes (avUCP, NRF1, NRF2, TFAM, PGC-1α), oxidative damage index (MDA, ROS, PC, 8-OHdG), and MMP level in chicken breast meat as compared to the CON group. These results indicate that dietary BS fmbj in broiler diets can protect breast meat against the storage-induced oxidative stress by improving their free radical scavenging capacity and antioxidant activity during 8 days of storage at 4°C.

Photoproduction of One-Electron Reducing Intermediates by Chromophoric Dissolved Organic Matter (CDOM): Relation to O2- and H2O2 Photoproduction and CDOM Photooxidation

A molecular probe, 3-amino-2,2,5,5,-tetramethy-1-pyrrolydinyloxy (3ap), was employed to determine the formation rates of one-electron reducing intermediates generated photochemically from both untreated and borohydride-reduced Suwanee River fulvic and humic acids (SRFA and SRHA, respectively). This stable nitroxyl radical reacts rapidly with reducing radicals and other one-electron reductants to produce a relatively stable product, the hydroxylamine, which can be derivatized with fluorescamine, separated by HPLC and quantified fluorimetrically. We provide evidence that O₂ and 3ap compete for the same pool(s) of photoproduced reducing intermediates, and that under appropriate experimental conditions, the initial rate of hydroxylamine formation (R_H) can provide an estimate of the initial rate of superoxide (O₂^-) formation. However, comparison of the initial rates of H₂O₂ formation (R_H2O2) to that of R_H show far larger ratios of R_H/R_H2O2 (∼6-13) than be accounted for by simple O₂^- dismutation (R_H/R_H2O2 = 2), implying a significant oxidative sink of O₂^- (∼67-85%). Because of their high reactivity with O₂^- and their likely importance in the photochemistry of CDOM, we suggest that coproduced phenoxy radicals could represent a viable oxidative sink. Because O₂^-/phenoxy radical reactions can lead to more highly oxidized products, O₂^- could be playing a far more significant role in the photooxidation of CDOM than has been previously recognized.

Assessment of the roles of reactive oxygen species in the UV and visible light photocatalytic degradation of cyanotoxins and water taste and odor compounds using C-TiO2

Visible light (VIS) photocatalysis has large potential as a sustainable water treatment process, however the reaction pathways and degradation processes of organic pollutants are not yet clearly defined. The presence of cyanobacteria cause water quality problems since several genera can produce potent cyanotoxins, harmful to human health. In addition, cyanobacteria produce taste and odor compounds, which pose serious aesthetic problems in drinking water. Although photocatalytic degradation of cyanotoxins and taste and odor compounds have been reported under UV-A light in the presence of TiO2, limited studies have been reported on their degradation pathways by VIS photocatalysis of these problematic compounds. The main objectives of this work were to study the VIS photocatalytic degradation process, define the reactive oxygen species (ROS) involved and elucidate the reaction mechanisms. We report carbon doped TiO2 (C-TiO2) under VIS leads to the slow degradation of cyanotoxins, microcystin-LR (MC-LR) and cylindrospermopsin (CYN), while taste and odor compounds, geosmin and 2-methylisoborneol, were not appreciably degraded. Further studies were carried-out employing several specific radical scavengers (potassium bromide, isopropyl alcohol, sodium azide, superoxide dismutase and catalase) and probes (coumarin) to assess the role of different ROS (hydroxyl radical OH, singlet oxygen (1)O2, superoxide radical anion [Formula: see text] ) in the degradation processes. Reaction pathways of MC-LR and CYN were defined through identification and monitoring of intermediates using liquid chromatography tandem mass spectrometry (LC-MS/MS) for VIS in comparison with UV-A photocatalytic treatment. The effects of scavengers and probes on the degradation process under VIS, as well as the differences in product distributions under VIS and UV-A, suggested that the main species in VIS photocatalysis is [Formula: see text] , with OH and (1)O2 playing minor roles in the degradation.

Photodynamic therapy: current status and future directions

Photodynamic therapy (PDT) is a minimally invasive therapeutic modality used for the management of a variety of cancers and benign diseases. The destruction of unwanted cells and tissues in PDT is achieved by the use of visible or near-infrared radiation to activate a light-absorbing compound (a photosensitizer, PS), which, in the presence of molecular oxygen, leads to the production of singlet oxygen and other reactive oxygen species. These cytotoxic species damage and kill target cells. The development of new PSs with properties optimized for PDT applications is crucial for the improvement of the therapeutic outcome. This review outlines the principles of PDT and discusses the relationship between the structure and physicochemical properties of a PS, its cellular uptake and subcellular localization, and its effect on PDT outcome and efficacy.

Isolation, characterization, spectroscopic properties and quantum chemical computations of an important phytoalexin resveratrol as antioxidant component from Vitis labrusca L. and their chemical compositions

In this study, isolation and characterization of trans-resveratrol (RES) as an antioxidant compound were carried out from VLE, VLG and VLS. Furthermore, antioxidant activities were evaluated by using six different methods. Finally, total phenolic, flavonoid, ascorbic acid, anthocyanin, lycopene, β-carotene and vitamin E contents were carried out. In addition, the FT-IR, (13)C and (1)H NMR chemical shifts and UV-vis. spectra of trans-resveratrol were experimentally recorded. Quantum chemical computations such as the molecular geometry, vibrational frequencies, UV-vis. spectroscopic parameters, HOMOs-LUMOs energies, molecular electrostatic potential (MEP), natural bond orbitals (NBO) and nonlinear optics (NLO) properties of title molecule have been calculated by using DFT/B3PW91 method with 6-311++G(d,p) basis set in ground state for the first time. The obtained results show that the calculated spectroscopic data are in a good agreement with experimental data.

Oxidatively generated damage to cellular DNA by UVB and UVA radiation

This review article focuses on a critical survey of the main available information on the UVB and UVA oxidative reactions to cellular DNA as the result of direct interactions of UV photons, photosensitized pathways and biochemical responses including inflammation and bystander effects. UVA radiation appears to be much more efficient than UVB in inducing oxidatively generated damage to the bases and 2-deoxyribose moieties of DNA in isolated cells and skin. The UVA-induced generation of 8-oxo-7,8-dihydroguanine is mostly rationalized in terms of selective guanine oxidation by singlet oxygen generated through type II photosensitization mechanism. In addition, hydroxyl radical whose formation may be accounted for by metal-catalyzed Haber-Weiss reactions subsequent to the initial generation of superoxide anion radical contributes in a minor way to the DNA degradation. This leads to the formation of both oxidized purine and pyrimidine bases together with DNA single-strand breaks at the exclusion, however, of direct double-strand breaks. No evidence has been provided so far for the implication of delayed oxidative degradation pathways of cellular DNA. In that respect putative characteristic UVA-induced DNA damage could include single and more complex lesions arising from one-electron oxidation of the guanine base together with aldehyde adducts to amino-substituted nucleobases.

Uric acid and thiocyanate as competing substrates of lactoperoxidase

The physiological function of urate is poorly understood. It may act as a danger signal, an antioxidant, or a substrate for heme peroxidases. Whether it reacts sufficiently rapidly with lactoperoxidase (LPO) to act as a physiological substrate remains unknown. LPO is a mammalian peroxidase that plays a key role in the innate immune defense by oxidizing thiocyanate to the bactericidal and fungicidal agent hypothiocyanite. We now demonstrate that urate is a good substrate for bovine LPO. Urate was oxidized by LPO to produce the electrophilic intermediates dehydrourate and 5-hydroxyisourate, which decayed to allantoin. In the presence of superoxide, high yields of hydroperoxides were formed by LPO and urate. Using stopped-flow spectroscopy, we determined rate constants for the reaction of urate with compound I (k1 = 1.1 × 10(7) M(-1) s(-1)) and compound II (k2 = 8.5 × 10(3) M(-1) s(-1)). During urate oxidation, LPO was diverted from its peroxidase cycle because hydrogen peroxide reacted with compound II to give compound III. At physiologically relevant concentrations, urate competed effectively with thiocyanate, the main substrate of LPO for oxidation, and inhibited production of hypothiocyanite. Similarly, hypothiocyanite-dependent killing of Pseudomonas aeruginosa was inhibited by urate. Allantoin was present in human saliva and associated with the concentration of LPO. When hydrogen peroxide was added to saliva, oxidation of urate was dependent on its concentration and peroxidase activity. Our findings establish urate as a likely physiological substrate for LPO that will influence host defense and give rise to reactive electrophilic metabolites.

Rapid reaction of superoxide with insulin-tyrosyl radicals to generate a hydroperoxide with subsequent glutathione addition

Tyrosine (Tyr) residues are major sites of radical generation during protein oxidation. We used insulin as a model to study the kinetics, mechanisms, and products of the reactions of radiation-induced or enzyme-generated protein-tyrosyl radicals with superoxide to demonstrate the feasibility of these reactions under oxidative stress conditions. We found that insulin-tyrosyl radicals combined to form dimers, mostly via the tyrosine at position 14 on the α chain (Tyr14). However, in the presence of superoxide, dimerization was largely outcompeted by the reaction of superoxide with insulin-tyrosyl radicals. Using pulse radiolysis, we measured a second-order rate constant for the latter reaction of (6±1) × 10(8) M(-1) s(-1) at pH 7.3, representing the first measured rate constant for a protein-tyrosyl radical with superoxide. Mass-spectrometry-based product analyses revealed the addition of superoxide to the insulin-Tyr14 radical to form the hydroperoxide. Glutathione efficiently reduced the hydroperoxide to the corresponding monoxide and also subsequently underwent Michael addition to the monoxide to give a diglutathionylated protein adduct. Although much slower, conjugation of the backbone amide group can form a bicyclic Tyr-monoxide derivative, allowing the addition of only one glutathione molecule. These findings suggest that Tyr-hydroperoxides should readily form on proteins under oxidative stress conditions where protein radicals and superoxide are both generated and that these should form addition products with thiol compounds such as glutathione.

The molecular basis for the pharmacokinetics and pharmacodynamics of curcumin and its metabolites in relation to cancer

This review addresses the oncopharmacological properties of curcumin at the molecular level. First, the interactions between curcumin and its molecular targets are addressed on the basis of curcumin's distinct chemical properties, which include H-bond donating and accepting capacity of the β-dicarbonyl moiety and the phenylic hydroxyl groups, H-bond accepting capacity of the methoxy ethers, multivalent metal and nonmetal cation binding properties, high partition coefficient, rotamerization around multiple C-C bonds, and the ability to act as a Michael acceptor. Next, the in vitro chemical stability of curcumin is elaborated in the context of its susceptibility to photochemical and chemical modification and degradation (e.g., alkaline hydrolysis). Specific modification and degradatory pathways are provided, which mainly entail radical-based intermediates, and the in vitro catabolites are identified. The implications of curcumin's (photo)chemical instability are addressed in light of pharmaceutical curcumin preparations, the use of curcumin analogues, and implementation of nanoparticulate drug delivery systems. Furthermore, the pharmacokinetics of curcumin and its most important degradation products are detailed in light of curcumin's poor bioavailability. Particular emphasis is placed on xenobiotic phase I and II metabolism as well as excretion of curcumin in the intestines (first pass), the liver (second pass), and other organs in addition to the pharmacokinetics of curcumin metabolites and their systemic clearance. Lastly, a summary is provided of the clinical pharmacodynamics of curcumin followed by a detailed account of curcumin's direct molecular targets, whereby the phenotypical/biological changes induced in cancer cells upon completion of the curcumin-triggered signaling cascade(s) are addressed in the framework of the hallmarks of cancer. The direct molecular targets include the ErbB family of receptors, protein kinase C, enzymes involved in prostaglandin synthesis, vitamin D receptor, and DNA.

Ceruloplasmin is an endogenous inhibitor of myeloperoxidase

Myeloperoxidase is a neutrophil enzyme that promotes oxidative stress in numerous inflammatory pathologies. It uses hydrogen peroxide to catalyze the production of strong oxidants including chlorine bleach and free radicals. A physiological defense against the inappropriate action of this enzyme has yet to be identified. We found that myeloperoxidase oxidized 75% of the ascorbate in plasma from ceruloplasmin knock-out mice, but there was no significant loss in plasma from wild type animals. When myeloperoxidase was added to human plasma it became bound to other proteins and was reversibly inhibited. Ceruloplasmin was the predominant protein associated with myeloperoxidase. When the purified proteins were mixed, they became strongly but reversibly associated. Ceruloplasmin was a potent inhibitor of purified myeloperoxidase, inhibiting production of hypochlorous acid by 50% at 25 nm. Ceruloplasmin rapidly reduced Compound I, the Fe(V) redox intermediate of myeloperoxidase, to Compound II, which has Fe(IV) in its heme prosthetic groups. It also prevented the fast reduction of Compound II by tyrosine. In the presence of chloride and hydrogen peroxide, ceruloplasmin converted myeloperoxidase to Compound II and slowed its conversion back to the ferric enzyme. Collectively, our results indicate that ceruloplasmin inhibits myeloperoxidase by reducing Compound I and then trapping the enzyme as inactive Compound II. We propose that ceruloplasmin should provide a protective shield against inadvertent oxidant production by myeloperoxidase during inflammation.

Redox reactions and microbial killing in the neutrophil phagosome

SIGNIFICANCE

When neutrophils kill microorganisms, they ingest them into phagosomes and bombard them with a burst of reactive oxygen species.

RECENT ADVANCES

This review focuses on what oxidants are produced and how they kill. The neutrophil NADPH oxidase is activated and shuttles electrons from NADPH in the cytoplasm to oxygen in the phagosomal lumen. Superoxide is generated in the narrow space between the ingested organism and the phagosomal membrane and kinetic modeling indicates that it reaches a concentration of around 20 μM. Degranulation leads to a very high protein concentration with up to millimolar myeloperoxidase (MPO). MPO has many substrates, but its main phagosomal reactions should be to dismutate superoxide and, provided adequate chloride, catalyze efficient conversion of hydrogen peroxide to hypochlorous acid (HOCl). Studies with specific probes have shown that HOCl is produced in the phagosome and reacts with ingested bacteria. The amount generated should be high enough to kill. However, much of the HOCl reacts with phagosomal proteins. Generation of chloramines may contribute to killing, but the full consequences of this are not yet clear.

CRITICAL ISSUES

Isolated neutrophils kill most of the ingested microorganisms rapidly by an MPO-dependent mechanism that is almost certainly due to HOCl. However, individuals with MPO deficiency rarely have problems with infection. A possible explanation is that HOCl provides a frontline response that kills most of the microorganisms, with survivors killed by nonoxidative processes. The latter may deal adequately with low-level infection but with high exposure, more efficient HOCl-dependent killing is required.

FUTURE DIRECTIONS

Better quantification of HOCl and other oxidants in the phagosome should clarify their roles in antimicrobial action.

Protein tyrosine nitration: biochemical mechanisms and structural basis of functional effects

In proteins, the nitration of tyrosine residues to 3-nitro-tyrosine represents an oxidative post-translational modification that disrupts nitric oxide ((•)NO) signaling and skews metabolism towards pro-oxidant processes. Indeed, excess levels of reactive oxygen species in the presence of (•)NO or (•)NO-derived metabolites lead to the formation of nitrating species such as peroxynitrite. Thus, protein 3-nitrotyrosine has been established as a biomarker of cell, tissue, and systemic "nitroxidative stress". Moreover, tyrosine nitration modifies key properties of the amino acid: phenol group pK(a), redox potential, hydrophobicity, and volume. Thus, the incorporation of a nitro group (-NO(2)) into protein tyrosines can lead to profound structural and functional changes, some of which contribute to altered cell and tissue homeostasis. In this Account, I describe our current efforts to define (1) biologically-relevant mechanisms of protein tyrosine nitration and (2) how this modification can cause changes in protein structure and function at the molecular level. First, I underscore the relevance of protein tyrosine nitration via free-radical-mediated reactions (in both peroxynitrite-dependent and -independent pathways) involving a tyrosyl radical intermediate (Tyr(•)). This feature of the nitration process is critical because Tyr(•) can follow various fates, including the formation of 3-nitrotyrosine. Fast kinetic techniques, electron paramagnetic resonance (EPR) studies, bioanalytical methods, and kinetic simulations have all assisted in characterizing and fingerprinting the reactions of tyrosine with peroxynitrite and one-electron oxidants and its further evolution to 3-nitrotyrosine. Recent findings show that nitration of tyrosines in proteins associated with biomembranes is linked to the lipid peroxidation process via a connecting reaction that involves the one-electron oxidation of tyrosine by lipid peroxyl radicals (LOO(•)). Second, immunochemical and proteomic-based studies indicate that protein tyrosine nitration is a selective process in vitro and in vivo, preferentially directed to a subset of proteins, and within those proteins, typically one or two tyrosine residues are site-specifically modified. The nature and site(s) of formation of the proximal oxidizing or nitrating species, the physicochemical characteristics of the local microenvironment, and the structural features of the protein account for part of this selectivity. How this relatively subtle chemical modification in one tyrosine residue can sometimes cause dramatic changes in protein activity has remained elusive. Herein, I analyze recent structural biology data of two pure and homogenously nitrated mitochondrial proteins (i.e., cytochrome c and manganese superoxide dismutase, MnSOD) to illustrate regioselectivity and structural effects of tyrosine nitration and subsequent impact in protein loss- or even gain-of-function.

Human indoleamine 2,3-dioxygenase is a catalyst of physiological heme peroxidase reactions: implications for the inhibition of dioxygenase activity by hydrogen peroxide

The heme enzyme indoleamine 2,3-dioxygenase (IDO) is a key regulator of immune responses through catalyzing l-tryptophan (l-Trp) oxidation. Here, we show that hydrogen peroxide (H(2)O(2)) activates the peroxidase function of IDO to induce protein oxidation and inhibit dioxygenase activity. Exposure of IDO-expressing cells or recombinant human IDO (rIDO) to H(2)O(2) inhibited dioxygenase activity in a manner abrogated by l-Trp. Dioxygenase inhibition correlated with IDO-catalyzed H(2)O(2) consumption, compound I-mediated formation of protein-centered radicals, altered protein secondary structure, and opening of the distal heme pocket to promote nonproductive substrate binding; these changes were inhibited by l-Trp, the heme ligand cyanide, or free radical scavengers. Protection by l-Trp coincided with its oxidation into oxindolylalanine and kynurenine and the formation of a compound II-type ferryl-oxo heme. Physiological peroxidase substrates, ascorbate or tyrosine, enhanced rIDO-mediated H(2)O(2) consumption and attenuated H(2)O(2)-induced protein oxidation and dioxygenase inhibition. In the presence of H(2)O(2), rIDO catalytically consumed nitric oxide (NO) and utilized nitrite to promote 3-nitrotyrosine formation on IDO. The promotion of H(2)O(2) consumption by peroxidase substrates, NO consumption, and IDO nitration was inhibited by l-Trp. This study identifies IDO as a heme peroxidase that, in the absence of substrates, self-inactivates dioxygenase activity via compound I-initiated protein oxidation. l-Trp protects against dioxygenase inactivation by reacting with compound I and retarding compound II reduction to suppress peroxidase turnover. Peroxidase-mediated dioxygenase inactivation, NO consumption, or protein nitration may modulate the biological actions of IDO expressed in inflammatory tissues where the levels of H(2)O(2) and NO are elevated and l-Trp is low.

Biologically relevant oxidants and terminology, classification and nomenclature of oxidatively generated damage to nucleobases and 2-deoxyribose in nucleic acids

A broad scientific community is involved in investigations aimed at delineating the mechanisms of formation and cellular processing of oxidatively generated damage to nucleic acids. Perhaps as a consequence of this breadth of research expertise, there are nomenclature problems for several of the oxidized bases including 8-oxo-7,8-dihydroguanine (8-oxoGua), a ubiquitous marker of almost every type of oxidative stress in cells. Efforts to standardize the nomenclature and abbreviations of the main DNA degradation products that arise from oxidative pathways are reported. Information is also provided on the main oxidative radicals, non-radical oxygen species, one-electron agents and enzymes involved in DNA degradation pathways as well in their targets and reactivity. A brief classification of oxidatively generated damage to DNA that may involve single modifications, tandem base modifications, intrastrand and interstrand cross-links together with DNA-protein cross-links and base adducts arising from the addition of lipid peroxides breakdown products is also included.

Spectral and kinetic evidence for reaction of superoxide with compound I of myeloperoxidase

Superoxide and myeloperoxidase (MPO) are essential for the oxidative killing of bacteria by neutrophils. Previously, we developed a kinetic model to demonstrate that within the confines of neutrophil phagosomes, superoxide should react exclusively with MPO and be converted to hypochlorous acid. The model consists of all known reactions and rate constants for reactions of superoxide, hydrogen peroxide, and chloride ions with MPO, except for the reaction of superoxide with compound I, which could only be estimated. Compound I is a transitory redox intermediate of MPO that is responsible for oxidizing chloride ions to hypochlorous acid. To tackle the challenge of observing the reaction between two transient species, we combined stopped-flow spectrophotometry with pulse radiolysis. Using this technique, we directly observed the reduction of compound I by superoxide. The rate constant for the reaction was determined to be 5.6±0.3×10(6)M(-1)s(-1). This value establishes superoxide as one of the best substrates for compound I. Based on this value, the rate constant for reduction of compound II by superoxide was determined to be 1.2±0.1×10(6)M(-1)s(-1). Within phagosomes, the reduction of compound I by superoxide will compete with the oxidation of chloride ions so that the relative concentrations of these two substrates will affect the yield of hypochlorous acid. Characterization of this reaction confirms that superoxide is a physiological substrate for MPO and that their interactions are central to an important host defense mechanism.

Inhibition of premature death by isothiocyanates through immune restoration in LP-BM5 leukemia retrovirus-infected C57BL/6 mice

The purpose of this study was to determine the effect of isothiocyanates (ITCs) in delaying the progression of the murine immunodeficiency virus to murine AIDS, resulting in increased life span. Furthermore, we investigated the role of ITCs in modulating immune dysfunction caused by LP-BM5 retrovirus infection. Among the tested ITCs, oral administration of sulforaphane (SUL), benzyl isothiocyante (BITC), and phenethyl isothiocyanate (PEITC) showed the inhibition of premature death caused by LP-BM5 retrovirus infection, while indolo[3,2-b] carbazole (ICZ) and indole-3-carbinol (I3C) did not delay the progress of the LP-BM5 retrovirus to murine AIDS. Inhibition of premature death by BITC, PEITC, and SUL could be explained by restoration of the immune system and down regulation of free radicals. Dysfunction of T and B cell mitogenesis caused by retrovirus infection in primary cultured splenocytes has been partially recovered with administration of BITC, PEITC, and SUL. There was a shift from imbalanced cytokine production (increased Th2 and decreased Th1 cell cytokine production) into balanced Th1/Th2 cell secretion of cytokines under administration of these ITCs during the development of murine AIDS. Hepatic vitamin E level was significantly restored by administration of these ITCs, in accordance with reduced hepatic lipid peroxidation levels. This study suggests that certain types of ITCs have beneficial effects in preventing premature death during progression to murine AIDS by restoration of immune dysfunction and removal of excessive free radicals, implying that selective usage of ITCs would be helpful in retarding the progression from HIV infection to AIDS.

Utilizing hydroglycolic extract from myrobalan fruits to counteract reactive oxygen species

The hydroglycolic (HG) extract from 70% propylene glycol (PG) extraction of myrobalan fruits showed the most appreciable antioxidant efficiency towards 1,1-diphenyl-2-picrylhydrazyl (DPPH) in comparison to the extracts from 30, 50, 70 and 100% ethyl alcohol (EA), and 30, 50 and 100% PG . Its total polyphenols were also higher than others. The additional analysis of antioxidant power revealed that this HG extract was able to counteract the induced oxidation caused by hydrogen peroxide (H(2) O(2) ) and 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). The quantification for the antioxidant capacity of the extract showed it was equivalent to 93.78 mg of 6-hydroxy-2,5,7,8-tetramethychroman-2-carboxylic acid (Trolox) g(-1) by 2,2'-azino-bis(3-ethylbenzthiazoline-6-suphonic acid) diammonium (ABTS) assay, and was 140.17 mg ascorbic acid (AA) equivalent g(-1) and 107.50 mg Trolox equivalent g(-1) by photochemiluminescence (PCL) assay. The incorporation of the HG myrobalan extract into lotion and sunscreen lotion rendered these products to provide the similar antioxidant power as the extract alone.

Urate as a physiological substrate for myeloperoxidase: implications for hyperuricemia and inflammation

Urate and myeloperoxidase (MPO) are associated with adverse outcomes in cardiovascular disease. In this study, we assessed whether urate is a likely physiological substrate for MPO and if the products of their interaction have the potential to exacerbate inflammation. Urate was readily oxidized by MPO and hydrogen peroxide to 5-hydroxyisourate, which decayed to predominantly allantoin. The redox intermediates of MPO were reduced by urate with rate constants of 4.6 × 10(5) M(-1) s(-1) for compound I and 1.7 × 10(4) M(-1) s(-1) for compound II. Urate competed with chloride for oxidation by MPO and at hyperuricemic levels is expected to be a substantive substrate for the enzyme. Oxidation of urate promoted super-stoichiometric consumption of glutathione, which indicates that it is converted to a free radical intermediate. In combination with superoxide and hydrogen peroxide, MPO oxidized urate to a reactive hydroperoxide. This would form by addition of superoxide to the urate radical. Urate also enhanced MPO-dependent consumption of nitric oxide. In human plasma, stimulated neutrophils produced allantoin in a reaction dependent on the NADPH oxidase, MPO and superoxide. We propose that urate is a physiological substrate for MPO that is oxidized to the urate radical. The reactions of this radical with superoxide and nitric oxide provide a plausible link between urate and MPO in cardiovascular disease.

Cytokine toxicity in insulin-producing cells is mediated by nitro-oxidative stress-induced hydroxyl radical formation in mitochondria

Although nitric oxide (NO) and oxidative stress both contribute to proinflammatory cytokine toxicity in pancreatic β-cells during type 1 diabetes mellitus (T1DM) development, the interactions between NO and reactive oxygen species (ROS) in cytokine-mediated β-cell death have not been clarified. Exposure of insulin-producing RINm5F cells to IL-1β generated NO, while exposure to a combination of IL-1β, TNF-α, and IFN-γ, which simulates T1DM conditions, generated both NO and ROS. In theory, two reactions between NO and ROS are possible, one with the superoxide radical yielding peroxynitrite, and the other with hydrogen peroxide (H(2)O(2)) yielding hydroxyl radicals. Results of the present work exclude peroxynitrite involvement in cytokine toxicity to β-cells because its generation did not correlate with the toxic action of cytokines. On the other hand, we show that H(2)O(2), produced upon exposure of insulin-producing cell clones and primary rat islet cells to cytokines almost exclusively in the mitochondria, reacted in the presence of trace metal (Fe(++)) with NO forming highly toxic hydroxyl radicals, thus explaining the severe toxicity that causes apoptotic β-cell death. Expression of the H(2)O(2)-inactivating enzyme catalase in mitochondria protected against cytokine toxicity by preventing hydroxyl radical formation. We therefore conclude that proinflammatory cytokine-mediated β-cell death is due to nitro-oxidative stress-mediated hydroxyl radical formation in the mitochondria.

Standardized extract of Dicksonia sellowiana Presl. Hook (Dicksoniaceae) decreases oxidative damage in cultured endothelial cells and in rats

AIMS

Aging and a variety of pathologies, including cancer, diabetes, cardiovascular and inflammatory diseases have been associated with reactive oxygen species (ROS), such as superoxide anion (O₂·⁻), hydroxyl radical (·OH) and hydrogen peroxide (H₂O₂) generation. Plant polyphenols bear radical scavenging/antioxidant activity. A phytomedicinal preparation obtained from aerial parts of Dicksonia sellowiana (Dicksoniaceae), a native plant from Central and South America, has been widely used in Brazil against asthma and presents beneficial effects in several other diseases, including cardiovascular disturbance. In this work, we investigated whether Dicksonia sellowiana, which is also known to contain high levels of polyphenols, presents antioxidant activity.

METHODS

The antioxidant activity of the hydroalcoholic extract obtained from Dicksonia sellowiana leaves (HEDS) was investigated by in vitro and in vivo tests.

RESULTS

HEDS (0.1-100 μg/mL) exhibited a strong scavenging activity against all reactive species tested (DPPH, O₂·⁻,·OH and H₂O₂; IC₅₀=6.83±2.05, 11.6±5.4, 2.03±0.4, and 4.8±0.4 μg/mL, respectively). HEDS strongly protected endothelial cells against H₂O₂-induced oxidative stress by mechanisms other than increasing catalase activity. In addition, HEDS protected cell membrane from oxidative damage. HEDS, (20 and 40 mg/kg) inhibited lipid peroxidation in vivo (29.8% and 24.5%, respectively).

CONCLUSIONS

According to our results, we can speculate that the traditional uses of Dicksonia sellowiana for cardiovascular diseases, asthma and skin diseases could be, at least in part, related to the potent antioxidant and endothelial protective activities of the plant.

Free radical scavenging, antioxidant enzymes and wound healing activities of leaves extracts from Clerodendrum infortunatum L

Three successive extracts of Clerodendrum infortunatum L. leaves have been studied for their potential as antioxidants in 1,1-diphenyl-2-picrylhydrazyl (DPPH) model. The scavenging activity of ethanol extract was found to be high when compared to petroleum ether and chloroform extracts. Hence, it was selected to evaluate the beneficial properties using in vitro and in vivo models. The antioxidant and its protective effects against CCl(4) induced oxidative stress in rats were significantly high. Further, to validate the traditional therapeutic claim, wound healing activity of the plant extracts was also carried out. Among the three extracts tested the petroleum ether and ethanol extracts exhibited a significant response. The presence of high antioxidant and pharmacological properties correlates to the total phenolic contents in the plant Clerodendrum infortunatum L.

Reactions of superoxide with the myoglobin tyrosyl radical

The contribution of superoxide-mediated injury to oxidative stress is not fully understood. A potential mechanism is the reaction of superoxide with tyrosyl radicals, which either results in repair of the tyrosine or formation of tyrosine hydroperoxide by addition. Whether these reactions occur with protein tyrosyl radicals is of interest because they could alter protein structure or modulate enzyme activity. Here, we have used a xanthine oxidase/acetaldehyde system to generate tyrosyl radicals on sperm whale myoglobin in the presence of superoxide. Using mass spectrometry we found that superoxide prevented myoglobin dimer formation by repairing the protein tyrosyl radical. An addition product of superoxide at Tyr151 was also identified, and exogenous lysine promoted the formation of this product. In our system, reaction of tyrosyl radicals with superoxide was favored over dimer formation with the ratio of repair to addition being approximately 10:1. Our results demonstrate that reaction of superoxide with protein tyrosyl radicals occurs and may play a role in free radical-mediated protein injury.

Serotonin as a physiological substrate for myeloperoxidase and its superoxide-dependent oxidation to cytotoxic tryptamine-4,5-dione

During inflammatory events, neutrophils and platelets interact to release a variety of mediators. Neutrophils generate superoxide and hydrogen peroxide, and also discharge the haem enzyme myeloperoxidase. Among numerous other mediators, platelets liberate serotonin (5-hydroxytryptamine), which is a classical neurotransmitter and vasoactive amine that has significant effects on inflammation and immunity. In the present study, we show that serotonin is a favoured substrate for myeloperoxidase because other physiological substrates for this enzyme, including chloride, did not affect its rate of oxidation. At low micromolar concentrations, serotonin enhanced hypochlorous acid production by both purified myeloperoxidase and neutrophils. At higher concentrations, it almost completely blocked the formation of hypochlorous acid. Serotonin was oxidized to a dimer by myeloperoxidase and hydrogen peroxide. It was also converted into tryptamine-4,5-dione, especially in the presence of superoxide. This toxic quinone was produced by stimulated neutrophils in a reaction that required myeloperoxidase. In plasma, stimulated human neutrophils oxidized serotonin to its dimer using the NADPH oxidase and myeloperoxidase. We propose that myeloperoxidase will oxidize serotonin at sites of inflammation. In doing so, it will impair its physiological functions and generate a toxic metabolite that will exacerbate inflammatory tissue damage. Consequently, oxidation of serotonin by myeloperoxidase may profoundly influence inflammatory processes.

Nordihydroguaiaretic acid is a potentin vitroscavenger of peroxynitrite, singlet oxygen, hydroxyl radical, superoxide anion and hypochlorous acid and preventsin vivoozone-induced tyrosine nitration in lungs

The antioxidant nordihydroguaiaretic acid (NDGA) has recently become well known as a putative anticancer drug. In this paper, it was evaluated the in vitro peroxynitrite (ONOO(-)), singlet oxygen ((1)O(2)), hydroxyl radical (OH(v)), hydrogen peroxide (H(2)O(2)), superoxide anion and hypochlorous acid (HOCl) scavenging capacity of NDGA. It was found that NDGA scavenges: (a) ONOO(-) (IC(50) = 4 +/- 0.94 microM) as efficiently as uric acid; (b) (1)O(2) (IC(50) = 151 +/- 20 microM) more efficiently than dimethyl thiourea, lipoic acid, N-acetyl-cysteine and glutathione; (c) OH(v) (IC(50) = 0.15 +/- 0.02 microM) more efficiently than dimethyl thiourea, uric acid, trolox, dimethyl sulfoxide and mannitol, (d) (IC(50) = 15 +/- 1 microM) more efficiently than N-acetyl-cysteine, glutathione, tempol and deferoxamine and (e) HOCl (IC(50) = 622 +/- 42 microM) as efficiently as lipoic acid and N-acetyl-cysteine. NDGA was unable to scavenge H(2)O(2). In an in vivo study in rats, NDGA was able to prevent ozone-induced tyrosine nitration in lungs. It is concluded that NDGA is a potent in vitro scavenger of ONOO(-), (1)O(2), OH(v), and HOCl and is able to prevent lung tyrosine nitration in vivo.